Polylactic acid-based resin compositions, molded articles and process for producing the same

ABSTRACT

A polylactic acid-based resin composition is provided from which molded articles with a high heat resistance and high impact strength can be molded with improved moldability. Also provided is a heat-resistant polylactic acid-based resin molded article manufactured from the polylactic acid-based resin composition, as well as a process for manufacturing such a heat-resistant molded article. A polylactic acid-based resin composition comprising 0.01 to 5.0 parts by weight of a metal phosphate and 0.01 to 5.0 parts by weight of a basic inorganic aluminum compound, each serving as a nucleating agent, with respect to 100 parts by weight of a polylactic acid-based polymer. The polylactic acid-based resin composition is melted and filled a mold of a molding machine set in a temperature range of not more than the crystallization-initiating point nor less than the glass transition point, as measured by a differential scanning calorimeter (DSC), to be molded the composition under crystallizing.

TECHNICAL FIELD

The present invention relates to a polylactic acid-based resincomposition from which articles with a high tensile strength, highimpact strength and high heat resistance can be molded with improvedmoldability, as well as to heat-resistant molded articles obtained fromsuch a resin composition. The present invention also relates to aprocess for producing the heat-resistant molded articles of thepolylactic acid-based resin.

The present invention further relates to a polylactic acid-basedstereocomplex polymer resin composition from which articles with a highheat resistance and a high impact resistance can be molded with improvedmoldability, as well as to heat-resistant molded articles obtained fromsuch a resin composition. The present invention also relates to aprocess for producing the heat-resistant molded articles of thepolylactic acid-based resin.

BACKGROUND ART

The growing concern for environmental protection has led to an increaseddemand for biodegradable polymers and molded articles thereof that candecompose when left in natural environment, and significant effort hasbeen devoted to the study of aliphatic polyesters and otherbiodegradable resins. Among others, polylactic acid-based polymers,which have a sufficiently high melting point of 140 to 180° C. and havean excellent transparency, are expected to find wide application inpackaging materials and other molded articles that can take advantage ofthe material's high transparency.

Despite its high rigidity, a container of a polylactic acid-basedpolymer formed by injection-molding and the like are susceptible toheat, or in some cases, to both heat and impact, and packagingcontainers, for example, are therefore not able to use with hot water ormicrowave oven. Thus, application of this material has been limited.

In order to impart sufficient heat resistance to such molded articles,the molds need to be cooled over a sufficiently long period of timeduring the molding process, or following the molding, the moldedarticles must be annealed to make them highly crystallized. However,such a long cooling process is impractical and often results ininsufficient crystallization and is thus disadvantageous, as is thepost-crystallization by annealing, in which molded articles tend todeform as they undergo crystallization.

As a method for increasing the rate of crystallization, for example,Japanese Patent Laid-Open Publication No. Sho 60-86156 is describedthat, fine powder of all-aromatic polyester that is composed mainly ofterephthalic acid and resorcin is added to serve as a nucleating agentfor promoting crystallization of polyethylene terephthalate (PET). Suchapproaches to facilitate the crystallization by the addition ofnucleating agents are well-known.

Also, examples of techniques in which the aforementioned additives areadded to biodegradable polymers are disclosed in Japanese PatentLaid-Open Publication No. Hei 5-70696, Japanese Patent NationalPublication No. Hei 4-504731 (WO 90/01521), U.S. Pat. No. 5,180,765,Japanese Patent National Publication No. Hei 6-504799 (WO 92/04413),Japanese Patent Laid-Open Publication No. Hei 4-220456, and JapanesePatent Laid-Open Publication No. 2001-226571.

In one such technique disclosed in Japanese Patent Laid-Open PublicationNo. Hei 5-70696, 10 to 40% by weight of calcium carbonate or hydrousmagnesium silicate (talc) with an average particle size of 20 μm or lessis added to a biodegradable plastic, such aspoly-3-hydroxybutylate/poly-3-hydroxyvalerate copolymer,polycaprolactone and polylactic acid, as a material for plasticcontainers. In this technique, however, the inorganic filler comprisedin large amounts are intended to facilitate degradation of wastedbiodegradable plastics but not to promote the crystallization of thepolymer to thereby increase its heat resistance.

In another technique described in Japanese Patent National PublicationNo. Hei 4-504731 (WO 90/01521), an inorganic filler such as silica orkaolinite is added to a lactide thermoplastic to alter properties ofhardness, strength and temperature resistance of the plastic. In oneexample, 5 wt % of calcium lactate to serve as a nucleating agent wasblended for 5 minutes using a heat roll at 170° C., with a L/DL-lactidepolymer. The sheet so formed proved to have sufficient rigidity andstrength, opacity, as well as increased degree of crystallization.

Japanese Patent National Publication No. Hei 6-504799 (WO 92/04413)describes a lactate and a benzoate to serve as a nucleating agent. Inone example, 1% calcium lactate was added to a polylactide copolymer,and injection-molding is performed using a mold maintained at about 85°C. with a detention time of 2 minutes. However, because ofincompleteness of crystallization, the product was further annealed inthe mold at about 110 to 135° C. Also, Japanese Patent Laid-OpenPublication No. Hei 8-193165 is disclosed in the paragraph numbered[0009] that, injection-molding was actually tried using a typicalnucleating agent, such as talc, silica, calcium lactate or sodiumbenzoate, had been added to a polylactic acid-based polymer. However,this technique failed to provide molded articles resistant to practicaluse since the crystallization rate was unfavorably slow and theresulting molded articles were brittle. The description further statesthat such polylactic acid-based polymers, when used in combination withtypical talc, silica or the like and subjected to general injectionmolding, blow molding, or compression-molding technique, underwentcrystallization at a significantly slow rate. In addition, the resultingmolded articles did not possess a practical heat resistance, allowingthe articles to be used only at temperatures not exceeding 100° C., nordid they exhibit a sufficient impact resistance. As a result,application of these materials was limited.

In still another technique described in Japanese Patent Laid-OpenPublication No. Hei 4-220456, a polyglycolic acid and/or its derivativeto serve as a nucleating agent is added to poly-L-lactide to increasethe crystallization rate. According to this technique, the cycle time ofinjection molding can be reduced and polymers with improved mechanicalproperties can be obtained. In one exemplary injection molding process,the degree of crystallization was 22.6% with the cooling time of 60seconds and with no nucleating agent added, whereas the degree ofcrystallization was 45.5% with a nucleating agent added. According tothe description in the paragraph numbered [0010] of Japanese PatentLaid-Open Publication No. Hei 8-193165, however, molding wasunsuccessful when a polylactic acid-based polymer was actuallyinjection-molded without any nucleating agents, under the condition ofthe mold temperature above the glass transition temperature as describedin Japanese Patent Laid-Open Publication No. Hei 4-220456.

In yet another technique described in Japanese Patent Laid-OpenPublication No. 2001-226571, a sorbitol compound or a metal phosphate toserve as a nucleating agent was added to a polylactic acid-based polymerto form heat-shrinkable film, in which a heat-shrinking property wasimproved. The nucleating agent described in this publication wasprovided in the form of a single compound, rather than a combinedsystem, and nothing was mentioned concerning stereo polymers.

DISCLOSURE OF THE INVENTION

Object of the Invention

In view of the aforementioned drawbacks of prior art, it is an objectiveof the present invention to provide a polylactic acid-based resincomposition that makes it possible to make molded articles having a hightensile strength, high impact strength and high heat resistance withimproved moldability. It is also an objective of the present inventionto provide molded articles that are formed of the polylactic acid-basedresin composition and thus have a high heat resistance as well as hightensile strength and high impact strength. It is a further objective ofthe present invention to provide a process for manufacturing moldedarticles of the polylactic acid-based resin that have a high heatresistance as well as high tensile strength, and high impact strength,from the polylactic acid-based resin compositions.

It is another objective of the present invention to provide a polylacticacid-based stereocomplex polymer resin composition that makes itpossible to make molded articles with a high heat resistance and highimpact resistance with improved moldability. It is still anotherobjective of the present invention to provide molded articles that areformed of the polylactic acid-based resin composition and thus have ahigh heat resistance and a high impact resistance. It is still yetanother objective of the present invention to provide a process formanufacturing molded articles of the polylactic acid-based resin thathave a high heat resistance and a high impact resistance from thepolylactic acid-based resin compositions.

SUMMARY OF THE INVENTION

Over the course of studies, the present inventors have found that theabove-described objectives of the present invention can be achievedthrough the use of a metal salt of an aromatic organic phosphate and abasic inorganic aluminum compound and, optionally, of at least one of adibenzylidene sorbitol compound and a metal salt of an aliphaticcarboxylic acid, and, further optionally, of talc. Each of thesecomponents serves as a nucleating agent for crystallization. Thisfinding ultimately led the present inventors to devise the presentinvention.

Over the course of studies, the present inventors have also found thatthe above-described objectives of the present invention can be achievedby adding a metal phosphate and, further favorably, hydrous magnesiumsilicate (talc), each serving as a nucleating agent, to a polymercapable of forming a stereocomplex composed mainly of polylactic acid.This finding ultimately led the present inventors to devise the presentinvention.

First Aspect of the Present Invention:

The present invention is a polylactic acid-based resin compositioncomprising 0.01 to 5.0 parts by weight of a metal phosphate and 0.01 to5.0 parts by weight of a basic inorganic aluminum compound, each servingas a nucleating agent, with respect to 100 parts by weight of apolylactic acid-based polymer.

The present invention is the above-described polylactic acid-based resincomposition wherein the metal phosphate comprises at least one metalsalt of an aromatic organic phosphate represented either by thefollowing general formula (1):

wherein R₁ represents a hydrogen atom or an alkyl group having 1 to 4carbon atoms; R₂ and R₃ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₁ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₁ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₁ is an aluminum atom, or by the following general formula (2):

wherein R₄, R₅, and R₆ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₂ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.

The present invention is the above-described polylactic acid-based resincomposition further comprising as the nucleating agent at least oneselected from the group consisting of a dibenzylidene sorbitol compoundrepresented by the following general formula (3) and a metal salt of analiphatic carboxylic acid:

wherein R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms; and R₉ and R₁₀ each independently representa hydrogen atom or an alkyl group having 1 to 4 carbon atoms and may ormay not be identical to each other, provided that at least one of R₉ andR₁₀ is an alkyl having group 1 to 4 carbon atoms.

The present invention is the above-described polylactic acid-based resincomposition, wherein the basic inorganic aluminum compound is at leastone selected from the group consisting of aluminum hydroxide, aluminumoxide, aluminum carbonate, and hydrotalcite compound. The presentinvention is the above-described polylactic acid-based resincomposition, wherein the hydrotalcite compound is represented by thefollowing general formula (4):Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4)wherein a is a number from 0 to 5.0; b is a number from 0 to 3.0; c is anumber from 0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a numberfrom 0 to 30. The present invention is the above-described polylacticacid-based resin composition, wherein the hydrotalcite compound is alithium-containing hydrotalcite compound with the amount a in thegeneral formula (4) being in the range from 0.1 to 5.

The present invention is the above-described polylactic acid-based resincomposition, further comprising hydrous magnesium silicate (talc). Thepresent invention is the above-described polylactic acid-based resincomposition, wherein the hydrous magnesium silicate (talc) has anaverage particle size of 10 μm or less.

The present invention is a heat-resistant molded article of polylacticacid-based resin obtained by molding any of the aforementionedpolylactic acid-based resin compositions.

The present invention is a method for producing a heat-resistant moldedarticle of polylactic acid-based resin, involving the steps of:

-   -   melting any of the above-described polylactic acid-based resin        composition,    -   filling a mold of a molding machine set in a temperature range        of not more than the crystallization-initiating point nor less        than the glass transition point, as measured by a differential        scanning calorimeter (DSC), with the composition, and    -   molding the composition under crystallizing.

The present invention is the above-described method for producing aheat-resistant molded article of polylactic acid-based resin, whereinthe temperature of the mold is set in a temperature range of not morethan the crystallization-initiating point nor less than thecrystallization-terminating point, as measured by a differentialscanning calorimeter (DSC).

Second Aspect of the Present Invention:

Also, the present invention is a polylactic acid-based resin compositioncomprising 100 parts by weight of a polylactic acid-based polymer and0.01 to 5.0 parts by weight of a nucleating agent, and having acrystallization peak temperature measured by a differential scanningcalorimeter (DSC) within the range of 90 to 120° C. and a heat ofcrystallization of 20 J/g or more.

The present invention is the above-described polylactic acid-based resincomposition comprising as the nucleating agent at least one selectedfrom the group consisting of a metal phosphate and a basic inorganicaluminum compound.

The present invention is the above-described polylactic acid-based resincomposition wherein the metal phosphate comprises at least one metalsalt of an aromatic organic phosphate represented either by thefollowing general formula (1):

wherein R₁ represents a hydrogen atom or an alkyl group having 1 to 4carbon atoms; R₂ and R₃ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₁ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₁ is an alkali metal atom, analkaline earth metal atom or a zinc atom while q is an integer of 1 or 2when M₁ is an aluminum atom, or by the following general formula (2):

wherein R₄, R₅, and R₆ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₂ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.

The present invention is the above-described polylactic acid-based resincomposition further comprising as the nucleating agent at least oneselected from the group consisting of a dibenzylidene sorbitol compoundrepresented by the following general formula (3) and a metal salt of analiphatic carboxylic acid:

wherein R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms; and R₉ and R₁₀ each independently representa hydrogen atom or an alkyl group having 1 to 4 carbon atoms and may ormay not be identical to each other, provided that at least one of R₉ andR₁₀ is an alkyl group having 1 to 4 carbon atoms.

The present invention is the above-described polylactic acid-based resincomposition, wherein the basic inorganic aluminum compound is at leastone selected from the group consisting of aluminum hydroxide, aluminumoxide, aluminum carbonate, and hydrotalcite compound. The presentinvention is the above-described polylactic acid-based resincomposition, wherein the hydrotalcite compound is represented by thefollowing general formula (4):Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4)wherein a is a number from 0 to 5.0; b is a number from 0 to 3.0; c is anumber from 0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a numberfrom 0 to 30. The present invention is the above-described polylacticacid-based resin composition, wherein the hydrotalcite compound is alithium-containing hydrotalcite compound with the amount a in thegeneral formula (4) being in the range from 0.1 to 5.

The present invention is the above-described polylactic acid-based resincomposition, further comprising hydrous magnesium silicate (talc). Thepresent invention is the above-described polylactic acid-based resincomposition, wherein the hydrous magnesium silicate (talc) has anaverage particle size of 10 μm or less.

The present invention is a heat-resistant molded article of polylacticacid-based resin obtained by molding any of the aforementionedpolylactic acid-based resin compositions.

The present invention is a method for producing a heat-resistant moldedarticle of polylactic acid-based resin, comprising the steps of:

-   -   melting any of the above-described polylactic acid-based resin        composition,    -   filling a mold of a molding machine set in a temperature range        of not more than the crystallization-initiating point nor less        than the glass transition point, as measured by a differential        scanning calorimeter (DSC), with the composition, and    -   molding the composition under crystallizing.

The present invention is the above-described method for producing aheat-resistant molded article of polylactic acid-based resin, whereinthe temperature of the mold is set in a temperature range of not morethan the crystallization-initiating point nor less than thecrystallization-terminating point, as measured by a differentialscanning calorimeter (DSC).

Third Aspect of the Present Invention:

Furthermore, the present invention is a polylactic acid-based resincomposition comprising 100 parts by weight of a polymer (A) which iscapable of forming a stereocomplex and is composed mainly of apolylactic acid comprising a poly-L-lactic acid composed mainly ofL-lactic acid and a poly-D-lactic acid composed mainly of D-lactic acid,and 0.01 to 5.0 parts by weight of a metal phosphate to serve as anucleating agent.

The present invention is the above-described polylactic acid-based resincomposition, further comprising 0.1 parts by weight or more of a hydrousmagnesium silicate (talc) to serve as the nucleating agent with respectto 100 parts by weight of the polymer (A). The present invention is theabove-described polylactic acid-based resin composition, wherein thehydrous magnesium silicate (talc) has an average particle size of 10 μmor less.

The present invention is the above-described polylactic acid-based resincomposition, wherein the poly-L-lactic acid composed mainly of L-lacticacid comprises 70 to 100 mol % of L-lactic acid units and 0 to 30 mol %of D-lactic acid units and/or copolymer units other than lactic acid,and/or, the poly-D-lactic acid composed mainly of D-lactic acidcomprises 70 to 100 mol % of D-lactic acid units and 0 to 30 mol % ofL-lactic acid units and/or copolymer units other than lactic acid.

The present invention is the above-described polylactic acid-based resincomposition, wherein the poly-L-lactic acid composed mainly of L-lacticacid has a weight average molecular weight of 50,000 to 500,000, and/or,the poly-D-lactic acid composed mainly of D-lactic acid has a weightaverage molecular weight of 50,000 to 500,000.

The present invention is the above-described polylactic acid-based resincomposition, wherein the blend ratio by weight of the poly-L-lactic acidto the poly-D-lactic acid is in the range of 10:90 to 90:10.

The present invention is the above-described polylactic acid-based resincomposition wherein the metal complex comprises at least one metal saltof an aromatic organic phosphate represented either by the followinggeneral formula

wherein R₁ represents a hydrogen atom or an alkyl group having 1 to 4carbon atoms; R₂ and R₃ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₁ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₁ is an alkali metal atom, analkaline earth metal atom or a zinc atom while q is an integer of 1 or 2when M₁ is an aluminum atom, or by the following general formula (2):

wherein R₄, R₅, and R₆ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₂ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.

The present invention is the above-described polylactic acid-based resincompound further comprising as the nucleating agent at least oneselected from the group consisting of a dibenzylidene sorbitol compoundrepresented by the following general formula (3), a basic inorganicaluminum compound, and a metal salt of an aliphatic carboxylic acid:

wherein R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms; and R₉ and R₁₀ each independently representa hydrogen atom or an alkyl group having 1 to 4 carbon atoms and may ormay not be identical to each other, provided that at least one of R₉ andR₁₀ is an alkyl group having 1 to 4 carbon atoms.

The present invention is the above-described polylactic acid-based resincomposition, wherein the basic inorganic aluminum compound is at leastone selected from the group consisting of aluminum hydroxide, aluminumoxide, aluminum carbonate, and hydrotalcite compound. The presentinvention is the above-described polylactic acid-based resincomposition, wherein the hydrotalcite compound is represented by thefollowing general formula (4):Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4)wherein a is a number from 0 to 5.0; b is a number from 0 to 3.0; c is anumber from 0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a numberfrom 0 to 30.

The present invention is the above-described polylactic acid-based resincomposition, wherein the polymer (A) which is capable of forming astereocomplex comprises an aliphatic polyester other than polylacticacid.

The present invention is a heat-resistant molded article of polylacticacid-based resin obtained by molding any of the aforementionedpolylactic acid-based resin compositions.

The present invention is a method for producing a heat-resistant moldedarticle of polylactic acid-based resin, comprising the steps of:

-   -   melting any of the above-described polylactic acid-based resin        composition,    -   filling a mold of a molding machine set in a temperature range        of not more than the melting point nor less than the glass        transition point, as measured by a differential scanning        calorimeter (DSC), with the composition, and    -   molding the composition under crystallizing.

The present invention is the above-described method for producing aheat-resistant molded article of polylactic acid-based resin, whereinthe temperature of the mold is set in a temperature range of not morethan the crystallization-initiating point nor less than thecrystallization-terminating point as measured by a differential scanningcalorimeter (DSC).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing temperature-lowering crystallization peakstaken on a DSC, observed in Examples 6 and 7 and Comparative Examples 4and 5.

MODES FOR CARRYING OUT THE INVENTION

First and Second Aspects of the Present Invention:

As used herein, the term “polylactic acid-based polymer” is meant toencompass not only homopolymer of polylactic acid but also copolymers ofpolylactic acid. The term also includes a blend polymer composing mainlyof homopolymer and/or copolymer of lactic acid.

In general, the polylactic acid-based polymer has a weight averagemolecular weight in the range of 50,000 to 500,000, and preferably inthe range of 100,000 to 250,000. The weight average molecular weightless than 50,000 cannot provide sufficient physical properties requiredfor practical use, whereas the weight average molecular weight greaterthan 500,000 tends to result in a decreased moldability.

While the molar ratio (L/D) of L-lactic acid units to D-lactic acidunits that constitute the polylactic acid-based polymer may be any valuebetween 100/0 to 0/100, it is preferred that either one unit of L-lacticacid or D-lactic acid is comprised in an amount of 75 mol % or more inorder to achieve a high melting point and in an amount of 90 mol % ormore in order to achieve an even higher melting point.

The copolymer of polylactic acid is formed by a monomer of lactic acidor lactide copolymerizes with other copolymerizable components. Examplesof these components include dicarboxylic acids, polyols,hydroxycarboxylic acids, and lactones and the like having 2 or morefunctional groups to form ester bonds, and various polyesters,polyethers and polycarbonates and the like formed of these components.

Examples of dicarboxylic acid include succinic acid, adipic acid,azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid andthe like.

Examples of polyol include aromatic polyols, such as those obtainedthrough the addition of ethylene oxide to bisphenol; aliphatic polyols,such as ethylene glycol, propylene glycol, butanediol, hexanediol,octanediol, glycerin, sorbitan, trimethylolpropane and neopentylglycol;ether glycols, such as diethylene glycol, triethylene glycol,polyethylene glycol and polypropylene glycol.

Examples of hydroxycarboxylic acid include glycolic acid,hydtoxybutylcarboxylic acid, and those described in Japanese PatentLaid-Open Publication No. Hei 6-184417.

Examples of lactone include glycolide, ε-caprolactoneglycolide,ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone,pivalolactone, and δ-valerolactone.

Polylactic acid-based polymers may be synthesized using knowntechniques: they may be synthesized through direct dehydrationcondensation of lactic acid monomers or through ring-openingpolymerization of cyclic lactide dimers of lactic acid as described inJapanese Patent Laid-Open Publication No. Hei 7-33861, Japanese PatentLaid-Open Publication No. Sho 59-96123, and Drafts for Symposium onMacromolecules Vol.44, pp.3198-3199.

In the case of direct dehydration condensation, any of L-lactic acid,D-lactic acid, DL-lactic acid, or mixtures thereof may be used, whereasany of L-lactide, D-lactide, DL-lactide, meso-lactide, or mixturesthereof may be used in the case of ring-opening polymerization.

Synthesis of lactides, purification and polymerization processes aredescribed in many literatures, including U.S. Pat. No. 4,057,537,European Patent Publication No. 261572, Polymer Bulletin, 14, 491-495(1985), and Makromol. Chem., 187, 1611-1628 (1986).

The catalysts for use in the polymerization reactions are not limitedand may be used any known catalyst for the polymerization of lacticacid. Examples include tin-based compounds such as tin lactate, tintartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tindistearate, tin dioleate, α-tin naphthoate, β-tin naphthoate and tinoctoate, powdered tin, and tin oxide; powdered zinc, zinc halide, zincoxide, and organozinc-based compounds; titanium-based compounds such astetrapropyl titanate; zirconium-based compounds such as zirconiumisopropoxide; antimony-based compounds such as antimony (III) oxide;bismuth-based compounds such as bismuth (III) oxide; and aluminum-basedcompounds such as aluminum oxide and aluminum isopropoxide.

Of these, the catalysts composed of tin or tin compounds areparticularly preferred in view of their activity. For example, in thecase of ring-opening polymerization, the catalyst is used in an amountof about 0.001 to 5% by weight with respect to the amount of lactide.

In general, the polymerization reaction may be carried out at atemperature of 100 to 220° C. in the presence of the above-describedcatalyst while reaction temperature may vary depending on the type ofthe catalyst. Alternatively, two-step polymerization may be carried outpreferably as described in Japanese Patent Laid-Open Publication No. Hei7-247345.

As used herein, the term “blend polymer” refers to a mixture obtained bymixing an aliphatic polyester other than polylactic acid into ahomopolymer of polylactic acid and/or a copolymer of polylactic acid andthen melting. Blending of the aliphatic polyester other than polylacticacid can impart a flexibility and impact resistance to the moldedarticles. The blending proportion by weight of the aliphatic polyesterother than polylactic acid is typically in the range of about 10 to 100parts by weight with respect to 100 parts by weight of the polylacticacid homopolymer and/or the lactic acid copolymer.

In the present invention, the aliphatic polyester other than polylacticacid (referred to simply as “aliphatic polyester”, hereinafter) may bemade up with a single polymer or it may be a composite of two or morepolymers. Among such polymers are polymers composed of an aliphaticcarboxylic acid component and an aliphatic alcohol component, andaliphatic hydroxycarboxylic acid polymers obtained through ring-openingpolymerization of cyclic anhydrides such as ε-caprolactone. These may beobtained either through the direct polymerization to produce highmolecular weight products or through an indirect approach in whichpolymerization is allowed to proceed until oligomers are formed and achain-extending agent and the like is subsequently used to produce highmolecular weight products. As long as the aliphatic polyester iscomposed mainly of the above-described aliphatic monomer components, itmay be either a copolymer or a mixture with other resins.

Preferably, the aliphatic polyester for use in the present inventioncomprises an aliphatic dicarboxylic acid and an aliphatic diol. Examplesof the aliphatic dicarboxylic acid include compounds such as succinicacid, adipic acid, suberic acid, sebacic acid and dodecanoic acid, andanhydrates and derivatives thereof. General examples of the aliphaticdiol include glycol-based compounds such as ethylene glycol, butanediol,hexanediol, octanediol and cyclohexanedimethanol, and derivativesthereof. Each of these aliphatic dicarboxylic acids and aliphatic diolsis a monomer compound with an alkylene group, cyclo group, or acycloalkylene group having 2 to 10 carbon atoms. The monomer compoundsselected from these aliphatic dicarboxylic acids and aliphatic diols aresubjected to condensation polymerization to produce the aliphaticpolyesters. Two or more of the monomer compounds may be used for each ofthe carboxylic acid components or the alcohol components.

To provide branches in the polymer to increase melt viscosity,polyfunctional carboxylic acids, alcohols or hydroxycarboxylic acidsthat have three or more functional groups may be used as a component ofthe aliphatic polyester. When used in excess, these components cause theformation of crosslinks in the resulting polymer and, as a result, thepolymer can lose its thermoplasticity or, even if it could retain somethermoplasticity, may form a microgel that is partially highlycrosslinked. For this reason, the component with three or morefunctional groups must be present in the polymer in a sufficiently smallamount that does not significantly affect the chemical and physicalproperties of the polymer. The polyfunctional component may be malicacid, tartaric acid, citric acid, trimellitic acid, pyromellitic acid,pentaerythrite, or trimethylolpropane.

Of the production methods of the aliphatic polyester, the directpolymerization technique is such that, with a proper selection of theaforementioned compounds, a high molecular weight product is obtainedwhile moisture present in the compounds or generated during thepolymerization is removed. The indirect polymerization, on the otherhand, is a technique in which the one selected from the above-describedcompounds is allowed to undergo polymerization until oligomers areformed and small amounts of chain-extending agents, includingdiisocyanate compounds such as hexamethylene diisocyanate, isophoronediisocyanate, xylylene diisocyanate and diphenylmethane diisocyanate,are then used to increase the molecular weight of the product. Anothertechnique involves the use of a carbonate compound to produce thealiphatic polyester carbonate.

The polylactic acid-based resin composition according to the firstaspect of the present invention comprises each of a metal phosphate anda basic inorganic aluminum compound in an amount of 0.01 to 5.0 parts byweight with respect to 100 parts by weight of a polylactic acid-basedpolymer.

The polylactic acid-based resin composition according to the secondaspect of the present invention comprises a nucleating agent forcrystallization in an amount of 0.01 to 10.0 parts by weight withrespect to 100 parts by weight of a polylactic acid-based polymer andhas a crystallization peak temperature in the range of 90 to 120° C. asmeasured by a differential scanning calorimeter (DSC) and a heat ofcrystallization of 20 J/g or more. Preferably, in this case, the resincomposition comprises a metal phosphate and/or a basic inorganicaluminum compound to serve as the nucleating agent for crystallization.

In the present invention, while the metal phosphate may be of any type,it preferably includes at least one of the metal salts of aromaticorganic phosphates represented by the general formula (1) or (2).

In the general formula (1), R₁ represents a hydrogen atom or an alkylgroup having 1 to 4 carbon atoms. Examples of the alkyl group having 1to 4 carbon atoms and represented by R₁ include methyl, ethyl, propyl,isopropyl, butyl, sec-butyl, and isobutyl. R₂ and R₃ each independentlyrepresent a hydrogen atom or an alkyl group having 1 to 12 carbon atomsand may or may not be identical to each other. Examples of the alkylgroup having 1 to 12 carbon atoms and represented by R₂ or R₃ includemethyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, amyl,tert-amyl, hexyl, heptyl, octyl, isooctyl, tert-octyl, 2-ethylhexyl,nonyl, isononyl, decyl, isodecyl, undecyl, dodecyl and tert-dodecyl. M₁represents an alkali metal atom, such as Li, Na and K, an alkaline earthmetal atom, such as Mg and Ca, a zinc atom, or an aluminum atom. p is aninteger of 1 or 2. q is an integer of 0 when M₁ is an alkali metal atom,an alkaline earth metal atom or a zinc atom while q is an integer of 1or 2 when M₁ is an aluminum atom.

Of the metal phosphates represented by the general formula (1),preferred are those in which R₁, R₂, and R₃ are H, t-butyl group, andt-butyl group, respectively.

In the general formula (2), R₄, R₅ and R₆ each independently represent ahydrogen atom or an alkyl group having 1 to 12 carbon atoms and may ormay not be identical to each other. The alkyl group having 1 to 12carbon atoms and represented by R₄, R₅ and R₆ may be the same as thoserepresented by R₂ and R₃ in the general formula (1). M₂ represents analkali metal atom, such as Li, Na and K, an alkaline earth metal atom,such as Mg and Ca, a zinc atom, or an aluminum atom. p is an integer of1 or 2. q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.

Of the metal phosphates represented by the general formula (2),preferred are those in which R₄, R₅, and R₆ are methyl group, t-butylgroup, and methyl group, respectively.

Some of the metal phosphates are commercially available, including Adekastab™ series NA-10, NA-11, NA-21, NA-30 and NA-35 manufactured by ASAHIDENKA Co., Ltd. Types and grades of the metal phosphates are suitablyselected depending on each application.

The metal salts of aromatic organic phosphate may be synthesized withoutparticular limitation and those synthesized using any known techniqueare allowed.

The basic inorganic aluminum compound for use in the present inventionis an inorganic aluminum compound having the ability to adsorb acidicsubstances. Examples include aluminum oxides, aluminum hydroxides,aluminum carbonates and hydrotalcites represented by the followingformula. These compounds may be used irrespective of the size andwhether the crystallization water is present or not:Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4)wherein a is a number from 0 to 5.0; b is a number from 0 to 3.0; c is anumber from 0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a numberfrom 0 to 30.

The hydrotarcite compounds for use in the present invention may beeither naturally-occurring or synthetic. Methods for synthesizing thecompound are described, for example, in Japanese Patent Publication No.Sho 46-2280, Japanese Patent Publication No. Sho 50-30039, JapanesePatent Publication No. Sho 51-29129, Japanese Patent Laid-OpenPublication No. Sho 61-174270, and Japanese Patent Laid-Open PublicationNo. Hei 6-248109. According to the present invention, the compound maybe used without any limitation on its crystal structure and crystalsize. Preferably, the compounds represented by the general formula (4)are used as the hydrotalcite compound. Particularly preferred of theseare the compounds containing Lithium. Specific examples include:

-   -   Li_(1.8)Mg₀.₆Al₄(OH)₁₈CO₃.3.6H₂O    -   Li₂Al₄(OH)₁₄CO₃.4H₂O    -   Li₁.₆Mg₁.₂Al₄(OH)₁₄CO₃    -   Li_(2.4)Mg_(0.3)Al₄(OH)₁₃CO₃. 4.6H₂O    -   Li_(3.2)Mg_(2.4)Al₂(OH)₁₂CO₃.3.3H₂O and    -   Li_(2.4)Mg_(0.8)Al₆(OH)₂₀CO₃.5.2H₂O,        and also include LMA manufactured by FUJI CHEMICAL Co., Ltd. as        commercially available products.

The surfaces of the hydrotalcite compound may be coated with a higherfatty acid such as stearic acid, a metal salt of a higher fatty acidsuch as an alkali metal salt of oleic acid, a metal salt of an organicsulfonic acid such as an alkali metal salt of dodecylbenzenesulfonicacid, a higher fatty acid amide, a higher fatty acid ester, or wax.

It is preferred that the polylactic acid-based resin composition of thepresent invention further comprises, in addition to the metal salt of anaromatic organic phosphate and the basic inorganic aluminum compound, atleast one selected from the dibenzylidene sorbitol compound representedby the general formula (3) and the metal salt of an aliphatic carboxylicacid as a nucleating agent for crystallization.

In the general formula (3) representing the dibenzylidene sorbitolcompound, R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4carbon atoms and represented by R₇ and R₈ include methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl, with methyl groupbeing preferred. R₉ and R₁₀ each independently represent a hydrogen atomor an alkyl group having 1 to 4 carbon atoms and may or may not beidentical to each other, provided that at least one of R₉ and R₁₀ is analkyl group having 1 to 4 carbon atoms. Examples of the alkyl grouphaving 1 to 4 carbon atoms and represented by R₉ and R₁₀ may be the sameas those represented by R₇ and R₈ with methyl group being preferred.Preferred dibenzylidene sorbitol compounds are those in which R₇, R₈,R₉, and R₁₀ are methyl group, H, methyl group, and H, respectively.

Examples of the aliphatic carboxylic acid to form the metal salt ofaliphatic carboxylic acid for use in the present invention includealiphatic carboxylic acids having 8 to 30 carbon atoms, such as octanoicacid, neooctanoic acid, decanoic acid, lauric acid, myristic acid,palmitic acid, stearic acid, oleic acid, ricinolic acid, behenic acid,and triacontanoic acid. Examples of the metal to form the metal salt ofaliphatic carboxylic acid include alkali metals such as lithium, sodium,and potassium; alkaline earth metals such as magnesium, calcium, andbarium; and other metals such as aluminum, lead, and zinc. While thesemetals may be either basic or neutral, they are preferably neutralsalts.

The metal salt of an aromatic organic phosphate and the basic inorganicaluminum compound, each serving as the nucleating agent forcrystallization in the present invention (first aspect), are each addedin an amount of 0.01 to 5.0 parts by weight, and preferably, in anamount of 0.1 to 3 parts by weight with respect to 100 parts by weightof the polylactic acid-based polymer. If the amount of each nucleatingagent is less than 0.01 parts by weight, then the desired effects ofadding the agent may not be obtained, whereas physical properties of themolded articles formed from the polylactic acid-based resin may becomeinsufficient if the amount of each nucleating agent exceeds 5.0 parts byweight. When at least one additional component, selected from thedibenzylidene sorbitol compound and the metal salt of an aliphaticcarboxylic acid, is added, in addition to the above-described metal saltof an aromatic organic phosphate and the basic inorganic aluminumcompound, to serve as the nucleating agent, each component may be usedin any desired amount. For example, the metal salt of an aromaticinorganic phosphate and the basic inorganic aluminum compound may makeup approximately 20 to 80% by weight of the total amount of thenucleating agents with the additional component accounting for theremainder. The amount and the proportion of the nucleating agents may beproperly selected depending on the type of the polylactic acid-basedpolymer and the desired molded article.

Preferably, the polylactic acid-based resin composition of the presentinvention further comprises hydrous magnesium silicate (i.e., talc),which may be of any type.

The hydrous magnesium silicate (talc) preferably has an average particlesize of 10 μm or less and, more preferably, from 1 to 5 μm. Althoughtalc with the average size larger than 10 μm exhibits some effects, talcthat is 10 μm or less in size has an improved ability to facilitate theformation of crystal nuclei, thus improving the heat resistance of themolded articles.

Preferably, the hydrous magnesium silicate (talc) is comprised in anamount of 0.01 to 5.0 parts by weight, more preferably, from 0.01 to 3.0parts by weight. When added in an amount less than 0.01 parts by weight,the hydrous magnesium silicate cannot provide desired effects, whereasit may cause turbidity in the resin composition when added in an amountof 5.0 parts by weight or more.

According to the present invention, each component of the nucleatingagent may be blended with the polylactic acid-based polymer using anyknown method. For example, powder or pellets of the polylacticacid-based polymer may be dry-blended with the components of thenucleating agent, or some of the components of the nucleating agent maybe pre-blended prior to the dry-blending of the other components. Forexample, the components may be mixed using a mill roll, a banbury mixer,a super mixer or other proper mixers, and kneaded with a uniaxial orbiaxial extruder or the like. In general, the mixing/kneading process iscarried out at temperatures of approximately 120 to 220° C. Thecomponents of the nucleating agent may be added during thepolymerization of the polylactic acid-based polymer. Alternatively, amaster batch comprising high concentrations of the components of thenucleating agent may be produced and added to the polylactic acid-basedpolymer.

When necessary, the polylactic acid-based resin composition of thepresent invention may further comprise various additives including aknown plasticizer, an antioxidant, a heat stabilizer, a photostabilizer,a UV-absorber, a pigment, a coloring agent, various fillers, anantistatic, a mold release agent, a perfume, a lubricant, aflame-retardant, a foaming agent, a bulking agent, anti-bacterial/fungalagent, and other nucleating agents.

As measured by a differential scanning calorimeter (DSC), the polylacticacid-based resin composition of the present invention has acrystallization peak temperature in the range of 90 to 120° C. andpreferably in the range of 95 to 115° C. and has a heat ofcrystallization of 20 J/g or more and preferably 21 J/g or more. Whileno specific upper limit is given for the heat of crystallization, it isapproximately 60 J/g. The crystallization peak temperature below 90° C.can result in an increase in the length of the cooling time during themolding process, whereas the crystallization peak temperature above 120°C. can lead to a higher mold temperature and thus a prolonged coolingtime. In either case, a longer molding cycle would result. Incomparison, if the heat of crystallization is less than 20 J/g, then themoldability of the resin composition at its crystallizing temperaturewill be decreased, as will the heat resistance, the tensile strength,and the impact strength of the resulting molded articles.

The metal salt of an aromatic organic phosphate and/or the basicinorganic aluminum compound, each preferably serving as the nucleatingagent in the present invention (second aspect), is added in an amount of0.01 to 5.0 parts by weight, and preferably, in an amount of 0.1 to 3parts by weight with respect to 100 parts by weight of the polylacticacid-based polymer. If the amount of each nucleating agent is less than0.01 parts by weight, then the desired effects of adding the agent maynot be obtained, whereas physical properties of the molded articlesformed from the polylactic acid-based resin may become insufficient ifthe amount of each nucleating agent exceeds 5.0 parts by weight. When atleast one additional component, selected from the dibenzylidene sorbitolcompound and the metal salt of an aliphatic carboxylic acid, is added,in addition to the above-described metal salt of an aromatic organicphosphate and/or the basic inorganic aluminum compound, to serve as thenucleating agent, each component may be used in any desired amount. Forexample, the metal salt of an aromatic inorganic phosphate and/or thebasic inorganic aluminum compound may make up approximately 20 to 80% byweight of the total amount of the nucleating agents with the additionalcomponent accounting for the remainder. The amount and the proportion ofthe nucleating agent may be properly selected depending on the type ofthe polylactic acid-based polymer and the desired molded article.

The present invention also concerns a heat-resistant molded article madefrom the above-described polylactic acid-based resin composition, aswell as a process for producing such a molded article.

One way to crystallize the polylactic acid-based resin composition is toanneal a molded article at a temperature that allows the resin tocrystallize. This approach, however, has a drawback that the moldedarticle tends to deform during the crystallization by annealing. Tocounteract this problem, the mold for use in molding the polylacticacid-based resin composition may be adjusted to a temperature thatallows the resin to crystallize and is retained at the temperature for apredetermined period of time.

According to the present invention, the polylactic acid-based resincomposition is first melted. A mold mounted on a molding machine is thenfilled with the molten resin. The mold is adjusted to a predeterminedtemperature that allows the resin composition to crystallize. Thistemperature lies in the range of not more than thecrystallization-initiating point nor less than the glass transitionpoint and preferably in the range of not more than thecrystallization-initiating point nor less than thecrystallization-terminating point, as measured by a differentialscanning calorimeter (DSC). The resin composition is subsequentlyretained in the mold for a predetermined period of time to allow it tomold with crystallization. Comprising the above-described nucleatingagent, the polylactic acid-based resin composition of the presentinvention undergoes crystallization in the mold to obtain a highlyheat/impact-resistant article of the polylactic acid-based resin.

Since the setting of the mold temperature may vary depending on the typeof the polylactic acid-based resin composition to be molded,crystallizing temperatures (i.e., crystallization peak temperature,crystallization-initiating temperature, and crystallization-terminatingtemperature) are measured in advance-using the DSC technique so that themold temperature may be adjusted to a temperature in the range of notmore than the crystallization-initiating temperature nor less than theglass transition temperature, preferably in the range of not more thanthe crystallization-initiating temperature nor less than thecrystallization-terminating temperature. With the mold temperaturefalling within this range, the resin composition can readily undergocrystallization and accurately sized molded articles can be obtained. Incontrast, if the mold temperature deviates from the above range,crystallization becomes slow and it takes longer for the resincomposition to solidify during the molding, resulting ininappropriateness for practical use.

In molding the polylactic acid-based resin composition of the presentinvention, the same molding techniques as used to mold common plastics,such as injection molding, blow molding, vacuum molding and compressionmolding, may be used to readily form bars, bottles, containers and othervarious molded articles.

Third Aspect of the Present Invention:

In the present invention, the polymer (A) capable of forming astereocomplex mainly comprises a polylactic acid comprising apoly-L-lactic acid composed mainly of L-lactic acid and a poly-D-lacticacid composed mainly of D-lactic acid. The polylactic acid may be anytype of polylactic acid that can form a stereocomplex and may bepolylactic acid homopolymer or polylactic acid copolymer. Also, thepolymer (A) capable of forming a stereocomplex may comprise otherpolymers, provided that it mainly comprises the polylactic acid capableof forming a stereocomplex.

It is preferred that the poly-L-lactic acid composed mainly of L-lacticacid comprises 70 to 100 mol %, preferably 90 to 100 mol %, of L-lacticacid unit and 0 to 30 mol %, preferably 0 to 10 mol %, of D-lactic acidunit and/or copolymer components other than lactic acid. Likewise, it ispreferred that the poly-D-lactic acid composed mainly of D-lactic acidcomprises 70 to 100%, preferably 90 to 100 mol %, of D-lactic acid unitand 0 to 30 mol %, preferably 0 to 10 mol %, of L-lactic acid unitand/or copolymer components other than lactic acid. The formation of thestereocomplexes is facilitated when both of the poly-L-lactic acidcomposed mainly of L-lactic acid and the poly-D-lactic acid composedmainly of D-lactic acid are made up with respective monomer units of theabove-specified range.

The poly-L-lactic acid preferably has a weight average molecular weightof 50,000 to 500,000, more preferably 100,000 to 250,000. Likewise, thepoly-D-lactic acid preferably has a weight average molecular weight of50,000 to 500,000, more preferably 100,000 to 250,000. If the weightaverage molecular weight of the poly-L-lactic acid or the poly-D-lacticacid is less than 50,000, then the resulting molded articles tend tohave a reduced strength, whereas, if the weight average molecular weightexceeds 500,000, the fluidity of the polymer composition is reduced,making the molding difficult.

While the mixing ratio by weight of the poly-L-lactic acid to thepoly-D-lactic acid may be any value, it is preferably in the range of10:90 to 90:10 (=(L):(D)). The formation of stereocomplexes isfacilitated when the mixing ratio falls within this range.

The poly-L-lactic acid may comprise at most 30 mol %, preferably at most10 mol %, of copolymer components other than lactic acid. Likewise, thepoly-D-lactic acid may comprise at most 30 mol %, preferably at most 10mol %, of copolymer components other than lactic acid. The monomercomponents to form the copolymer are monomers other than lactic acidthat can copolymerize with lactic acid monomers or lactides. Examples ofthe other monomer components include dicarboxylic acids, polyols,hydroxycarboxylic acids and lactones that have two or more functionalgroups capable of forming ester bonds, and various polyesters,polyethers and polycarbonates composed of these various components.These other monomer components are the same as those described in theforegoing sections of the first and the second aspects of the invention.

The poly-L-lactic acid and the poly-D-lactic acid may be synthesized byusing known techniques: they may be synthesized through directdehydration condensation or through ring-opening polymerization ofcyclic lactide dimers of lactic acid, as described in Japanese PatentLaid-Open Publication No. Hei 7-33861, Japanese Patent Laid-OpenPublication No. Sho 59-96123, and Drafts for Symposium on MacromoleculesVol.44, pp.3198-3199.

When the poly-L-lactic acid or the poly-D-lactic acid is obtainedthrough direct dehydration condensation, any of L-lactic acid, D-lacticacid, DL-lactic acid or a mixture thereof is used so that the monomerunits are present in the above-specified respective molar percentages.Likewise, when the poly-L-lactic acid or the poly-D-lactic acid isobtained through ring-opening polymerization, any of L-lactide,D-lactide, DL-lactide, meso-lactide or a mixture thereof is used so thatthe monomer units are present in the above-specified respective molarpercentages.

As for the catalysts for use in the polymerization reaction, they arethe same as those described in the foregoing sections of the first andthe second aspects of the invention, and are not limited to particularones. The catalyst may be any known catalyst commonly in use for lacticacid polymerization. The polymerization process is also the same asdescribed above.

The polymer (A) capable of forming a stereocomplex may comprise otherpolymers, provided that it mainly comprises the polylactic acid capableof forming a stereocomplex. One example of other polymer is aliphaticpolyesters other than polylactic acid, which are the same as thosedescribed in the foregoing sections of the first and the second aspectsof the invention. Blending the aliphatic polyester can impartflexibility and impact resistance to the molded articles. The proportionof the aliphatic polyester other than polylactic acid is typically inthe range of about 10 to 100 parts by weight with respect to 100 partsby weight of the polylactic acid.

The polylactic acid-based polymer composition of the present inventioncomprises at least one metal phosphate to serve as a nucleating agentfor crystallization in an amount of 0.01 to 5.0 parts by weight withrespect to 100 parts by weight of the polymer (A) capable of forming astereocomplex mainly comprising the polylactic acid. Preferably, thepolylactic acid-based resin composition further comprises 0.1 parts byweight or more of hydrous magnesium silicate (talc) with respect to 100parts by weight of the polymer (A).

According to the present invention, comprising of hydrous magnesiumsilicate (talc) in addition to the metal phosphate facilitates formationof crystal nuclei of the polymer composition. Not only does thisfacilitate the crystallization but it also reduces the crystal size andimproves the physical properties.

The hydrous magnesium silicate (talc) preferably has an average particlesize of 10 μm or less and more preferably, from 1 to 5 μm. Although thehydrous magnesium silicate (talc) with the average particle size of morethan 10 μm may have some effects, it can facilitate the formation ofcrystal nuclei more effectively and can effectively improve the heatresistance of the molded articles when having an average size of lessthan 10 μm.

The amount of the hydrous magnesium silicate (talc) to be blended ispreferably 0.1 parts by weigh or more, for example, from 0.1 to 5.0parts by weight, and more preferably, from 0.1 to 3.0 parts by weightwith respect to 100 parts by weight of the polymer (A) capable offorming a stereocomplex. When added in an amount of less than 0.1 partsby weight, adding the hydrous magnesium silicate may not exhibit desiredeffects, whereas it may cause turbidity in the polymer composition whenadded in an amount of 5.0 parts by weight or more, making the polymerunsuitable for use in molded articles that require a transparency.Alternatively, the hydrous magnesium silicate (talc) may be added in anamount of 5.0 parts by weight or more to serve as an inorganic filler toimprove the rigidity of the molded articles. In such a case, the amountof the hydrous magnesium silicate (talc) is properly selected from therange of 5.0 parts by weight to 100 parts by weight.

A preferred example of the metal phosphate for use in the presentinvention is a metal salt of an aromatic organic phosphate representedby the general formula (1) or (2). The metal salts of an aromaticorganic phosphate may be used either individually or in combination oftwo or more. The metal salts of an aromatic organic phosphaterepresented by the general formula (1) or (2) are the same as thosedescribed in the foregoing sections of the first and the second aspectsof the invention. Preferred examples are also the same as thosedescribed in these sections.

Aside from the metal salt of an aromatic organic phosphate, thepolylactic acid-based resin composition of the present inventionpreferably comprises at least one selected from dibenzylidene sorbitolcompounds represented by the general formula (3), basic inorganicaluminum compounds, and metal salts of aliphatic carboxylic acids. Thedibenzylidene sorbitol compounds represented by the general formula (3),the basic inorganic aluminum compounds, and the metal salts of aliphaticcarboxylic acids are the same respectively as those described in theforegoing sections of the first and the second aspects of the invention.Preferred examples are also the same respectively as those described inthese sections.

According to the present invention, the amount of the metal phosphate tobe blended is in the range of 0.01 to 5.0 parts by weight, preferably inthe range of 0.1 to 3 parts by weight, with respect to 100 parts byweight of the polymer (A) capable of forming a stereocomplex. If theamount of the metal phosphate is less than 0.01 parts by weight, thenthe desired effects of adding the agent may not be obtained, whereasphysical properties of the molded articles formed from the polylacticacid-based polymer may become insufficient if the amount exceeds 5.0parts by weight. Aside from the metal phosphate, at least one compoundselected from the dibenzylidene sorbitol compound, the basic inorganicaluminum compound, and the metal salt of an aliphatic carboxylic acidmay be used as an additional component. While this additional componentmay be used in any amount, it is preferably used in an amount of 0.1 to5.0 parts by weight with respect to 100 parts by weight of the polymer(A) and in an amount 0.1 to 10 times the amount of the metal phosphate.The amount and the proportion of the additional component may beproperly selected depending on the type of the polylactic acid-basedpolymer and the desired molded article.

According to the present invention, the metal phosphate may be blendedusing any known method, as may the optional components of the hydrousmagnesium silicate (talc), the dibenzylidene sorbitol compound, thebasic inorganic aluminum compound and the metal salt of an aliphaticcarboxylic acid. For example, the same methods as those described in theforegoing sections of the first and the second aspects of the inventionmay be employed.

When necessary, the polylactic acid-based resin composition of thepresent invention may further comprise various additives including aknown plasticizer, an antioxidant, a heat stabilizer, a photostabilizer,a UV-absorber, a pigment, a coloring agent, various fillers, anantistatic, a mold release agent, a perfume, a lubricant, aflame-retardant, a foaming agent, a bulking agent, anti-bacterial/fungalagent, and other nucleating agents.

The present invention further concerns a heat-resistant molded articlemade from the above-described polylactic acid-based resin composition,as well as a process for producing such a molded article.

One way to crystallize the polylactic acid-based resin composition is toanneal a molded article at a temperature that allows the resin tocrystallize. This approach, however, has a drawback that the moldedarticle tends to deform during the crystallization by annealing. Tocounteract this problem, the mold may be adjusted to a temperature thatallows the resin to crystallize and is retained at the temperature for apredetermined period of time.

According to the present invention, the polylactic acid-based resincomposition is first melted. A mold mounted on a molding machine is thenfilled with the molten resin. The mold is adjusted to a predeterminedtemperature that allows the resin composition to crystallize. Thistemperature lies in the range of not more than the melting point norless than, the glass transition point and preferably in the range of notmore than the crystallization-initiating point nor less than thecrystallization-terminating point, as measured by a differentialscanning calorimeter (DSC). The resin composition is subsequentlyretained in the mold for a predetermined period of time to allow it tomold with crystallization. Comprising the above-described metalphosphate and, in preferred cases, further comprising the hydrousmagnesium silicate (talc), the polylactic acid-based resin compositionof the present invention undergoes crystallization in the mold to obtaina highly heat/impact-resistant article of the polylactic acid-basedresin.

Since the setting of the mold temperature may vary depending on the typeof the polylactic acid-based resin composition to be molded,crystallizing temperatures (i.e., crystallization peak temperature,crystallization-initiating temperature, and crystallization-terminatingtemperature) are measured in advance using the DSC technique so that themold temperature may be adjusted to a temperature in the range of notmore than the melting point nor less than the glass transitiontemperature, preferably in the range of not more than thecrystallization-initiating temperature nor less than thecrystallization-terminating temperature. With the mold temperaturefalling within this range, the resin composition can readily undergocrystallization and accurately sized molded articles can be obtained. Incontrast, if the mold temperature deviates from the above range,crystallization becomes slow and it takes longer for the resincomposition to solidify during the molding, resulting ininappropriateness for practical use.

In molding the polylactic acid-based resin composition of the presentinvention, the same molding techniques as used to mold common plastics,such as injection molding, blow molding, vacuum molding and compressionmolding, may be used to readily form bars, bottles, containers and othervarious molded articles. In preferred embodiments of the presentinvention, it is important to use hydrous magnesium silicate (talc)along with the metal phosphate. When hydrous magnesium silicate (talc),a nucleating agent known to be effective for use with polylactic acid,is applied to the polymer capable of forming a stereocomplex, doublecrystallization peaks are observed, and, though the formation of crystalnuclei is promoted, the resulting crystal is a heterogeneous crystal inwhich stereo crystal and polylactic acid homo crystal are present. Themetal phosphate also promotes the crystallization of polylactic acid.When used alone, however, the metal phosphate brings about a lowercrystallization temperature and a lower crystallization rate than arepossible by the use of talc. It is only when the talc and the metalphosphate are together applied to the polymer capable of forming astereocomplex that a single crystallization peak is observed with a highcrystallization temperature and a high heat of crystallization. Also,the crystallized polymer obtained by this process has a melting point ofapproximately 210° C., which is significantly lower than the meltingpoint of conventional stereocomplex crystal of 230° C. Furthermore, thepolymer has an improved workability, which is the property that poses aproblem in molding conventional stereo polymers. The polymer alsoexhibits an improved heat resistance as compared to the conventionallactic acid homopolymer.

In each of the first, the second and the third aspects of the presentinvention, the crystallization temperature and the heat ofcrystallization were measured by a differential scanning calorimeter(DSC-60 manufactured by Shimadzu Corporation): 10 mg sample pellets wereheated from room temperature to 250° C. at a rate of 50° C./min, andwere retained for 5 minutes to make the sample uniform. Subsequently,the sample was allowed to cool at a rate of 5° C./min, during which timethe temperature at which crystallization was initiated, the temperatureat which crystallization peaked, and the temperature at whichcrystallization was terminated were measured. The magnitude of thecrystallization peak (heat of crystallization) so measured was then usedas an index of the heat resistance: a larger heat of crystallization ata process of cooling indicates a higher degree of crystallization andthus, a higher heat resistance. The melting point of the resultingcrystals was measured by again taking measurements by DSC at a processof reheating the sample until 250° C. at a rate of 10° C./min.

A tensile test and an Izod impact test were conducted according to JIS K7113 (No. 1 sample piece) and JIS K 7110 (notched No. 2 sample piece),respectively.

In the present invention, high-load distortion temperature according toJIS K 7207A standard was used as an index for the heat resistance. Asused herein, the term “high-load distortion temperature” refers to atemperature of a heat-conductive medium determined in the followingmanner: a sample piece immersed in a heat sink is applied a 1.8 MPabending stress while a heat conductive medium is heated at a constantrate. The temperature of the heat-conductive medium is measured when thesample piece is distorted by a predetermined amount, thus giving thehigh-load distortion temperature. According to the present invention,the molded articles of the heat-resistant polylactic acid-based resin,even when used, for example, in parts of home electric appliances thatare rarely exposed to high temperatures, need to have a high-loaddistortion temperature of 80° C. or above for practical use, preferably90° C. or above, and more preferably 100° C. or above, while thehigh-load distortion temperature may vary depending on the amount of thenucleating agent added. The upper limit thereof is not particularlyrestricted, but is 140° C. or around.

In the present invention, the weight average molecular weight (Mw) ofthe lactic acid-based polymer is measured by GPC analysis relative topolystyrene standard.

EXAMPLES

The present invention will now be described in further detail withreference to several examples, which are not intended to limit the scopeof the invention in any way.

Examples 1 through 5 are embodiments of the first and the second aspectsof the invention.

Example 1

A set of components shown in Table 1 were dry-blended with one another,and the mixture was melted and mixed in a biaxial kneading extruder at200° C. for an average time period of 4 minutes and was extruded from amouthpiece into strands. The strands were then water-cooled and cut intopellets of a polylactic acid-based polymer composition comprising anucleating agent. The measurements taken of the resulting pellets on aDSC gave a crystallization peak temperature of 105° C., acrystallization-initiating temperature of 116° C., acrystallization-terminating temperature of 95° C., and a heat ofcrystallization of 35 J/g.

The resulting pellets were vacuum-dried at 80° C. until absolutely dryand were then injection-molded with the mold temperature kept at 100° C.and the cooling time at 45 seconds. This gave a sample piece for theevaluation of physical properties according to JIS. The results of theevaluation of the sample piece are shown in Table 2 below.

Example 2

Pellets of another polylactic acid-based polymer composition wereobtained in the same manner as in Example 1, except that another set ofcomponents shown in Table 1 was used. The measurements taken of thepellets by the DSC gave a crystallization peak temperature of 114° C., acrystallization-initiating temperature of 125° C., acrystallization-terminating temperature of 104° C., and a heat ofcrystallization of 33 J/g. The pellets were injection-molded in the samemanner as in Example 1 to give another sample piece for the evaluationof the physical properties according to JIS. The results of theevaluation of the sample piece are shown in Table 2 below.

Example 3

Pellets of another polylactic acid-based polymer composition wereobtained in the same manner as in Example 1, except that another set ofcomponents shown in Table 1 was used. The measurements taken of thepellets by the DSC gave a crystallization peak temperature of 99° C., acrystallization-initiating temperature of 104° C., acrystallization-terminating temperature of 83° C., and a heat ofcrystallization of 28 J/g. The pellets were injection-molded in the samemanner as in Example 1 to give another sample piece for the evaluationof the physical properties according to JIS. The results of theevaluation of the sample piece are shown in Table 2 below.

Example 4

Pellets of another polylactic acid-based polymer composition wereobtained in the same manner as in Example 1, except that another set ofcomponents shown in Table 1 was used. The measurements taken of thepellets by the DSC gave a crystallization peak temperature of 112° C., acrystallization-initiating temperature of 122° C., acrystallization-terminating temperature of 101° C., and a heat ofcrystallization of 42 J/g. The pellets were injection-molded in the samemanner as in Example 1 to give another sample piece for the evaluationof the physical properties according to JIS. The results of theevaluation of the sample piece are shown in Table 2 below.

Example 5

Pellets of another polylactic acid-based polymer composition wereobtained in the same manner as in Example 1, except that another set ofcomponents shown in Table 1 was used. The measurements taken of thepellets by the DSC gave a crystallization peak temperature of 100° C., acrystallization-initiating temperature of 105° C., acrystallization-terminating temperature of 96° C., and a heat ofcrystallization of 25 J/g. The pellets were injection-molded in the samemanner as in Example 1 to give another sample piece for the evaluationof the physical properties according to JIS. The results of theevaluation of the sample piece are shown in Table 2 below.

Comparative Example 1

Polylactic acid shown in Table 1 was melted and mixed in a biaxialkneading extruder at 200° C. for an average time period of 4 minutes andwas extruded from a mouthpiece into strands. The strands were thenwater-cooled and cut into pellets of polylactic acid. The measurementstaken of the pellets on a DSC gave a crystallization peak temperature of99° C., a crystallization-initiating temperature of 112° C., acrystallization-terminating temperature of 85° C., and a heat ofcrystallization of 15 J/g.

The resulting pellets were vacuum-dried at 80° C. until absolutely dryand were then injection-molded with the mold temperature kept at 100° C.and the cooling time at 45 seconds. The molded product could not beremoved from the mold, however. Separately, the pellets werevacuum-dried at 80° C. until absolutely dry and were theninjection-molded with the mold temperature kept at 40° C. and thecooling time at 45 seconds. This gave a sample piece for the evaluationof physical properties according to JIS. The results of the evaluationof the sample piece are shown in Table 2 below.

Comparative Example 2

Pellets of a polylactic acid-based polymer composition were obtained inthe same manner as in Example 1, except that another set of componentsshown in Table 1 was used. The measurements taken of the pellets by theDSC gave a crystallization peak temperature of 101° C., acrystallization-initiating temperature of 115° C., acrystallization-terminating temperature of 90° C., and a heat ofcrystallization of 16 J/g. The resulting pellets were vacuum-dried at80° C. until absolutely dry and were then injection-molded with the moldtemperature kept at 100° C. and the cooling time at 45 seconds. Themolded product could not be removed from the mold, however. Separately,the pellets were vacuum-dried at 80° C. until absolutely dry and werethen injection-molded with the mold temperature kept at 40° C. and thecooling time at 45 seconds. This gave a sample piece for the evaluationof physical properties according to JIS. The results of the evaluationof the sample piece are shown in Table 2 below. TABLE 1 ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 1Example 2 parts by parts by parts by parts by parts by parts by parts bycompound weight weight weight weight weight weight weight poly-lacticacid 100 100 100 100 100 100 100 (“Lacty” manufactured by ShimadzuCorporation, Mw = 160,000) 1·3,2·4-di(p-methyl — — — — 0.2 — 1benzylidene sorbitol) aluminum bis(2,2′-methylene 0.5 0.5 0.5 0.5 0.5 —— bis-4,6-di-tert-butyl-phenyl phosphate)hydroxide lithium myristate — —0.1 0.1 0.1 — — hydrotalcite compound 0.5 0.5 0.4 0.4 0.4 — — talc finepowder — 1 — 1 — — — (“Micro Ace P-6”, manufactured by Nippon talc Co.,Ltd.)

TABLE 2 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 1 Example 2 peak crystallization 105 114 99 112 100 99101 temperature(° C.) heat of 35 33 28 42 25 15 16 crystallization (J/g)high-load distortion 110 119 107 118 107 58 58 temperature(° C.) tensilestrength 72 72 72 72 73 63 63 (Mpa) tensile modulus 3,188 3,258 3,2143,264 3,230 2,643 2,655 (MPa) Izod impact strength 3.1 3.3 3.0 3.3 3.12.6 2.7 (kJ/m²)

The results of Tables 1 and 2 indicate that the injection-moldedarticles made from the polylactic acid-based polymer compositions ofExamples 1 through 5, each an embodiment of the present invention, eachhad an improved heat resistance, tensile strength, tensile modulus, andIzod impact strength. The sample pieces of Examples 2 and 4, each ofwhich was made from the polylactic acid-based polymer compositioncomprising talc along with the nucleating agent, exhibited a higher heatresistance. On the other hand, in Comparative Example 1, which did notcomprise the nucleating agent, exhibited a significant decrease in themoldability as well as heat resistance and strength of the moldedarticle. Though comprising the nucleating agent, because of the smallheat of crystallization, Comparative Example 2 showed a significantdecrease in the moldability as well as heat resistance and strength ofthe molded article.

Examples 6 and 7 are embodiments of the third aspect of the invention.

Example 6

50 parts by weight of poly-L-lactic acid (“Lacty” manufactured byShimadzu Corporation, Mw=180,000), 50 parts by weight of poly-D-lacticacid synthesized from D-lactide (Mw=180,000), 0.5 parts by weight ofaluminum bis(2,2′-methylenebis-(4,6-di-tert-butyl-phenyl)phosphate)hydroxide, 0.2 parts by weight of lithium myristate, and 0.3 parts byweight of Li_(1.8)Mg_(0.6)Al₄(OH)₁₈CO₃.3.6H₂O, a lithium-containinghydrotalcite compound, were dry-blended with one another, and themixture was melted and mixed in a biaxial kneading extruder at 220° C.for an average detention time period of 4 minutes and was extruded froma mouthpiece into strands. The strands were then water-cooled to obtaina chip C1 of a lactic acid-based stereo polymer composition.

The measurements taken of the chip C1 on a DSC gave a crystallizationpeak temperature of 143° C., a crystallization-initiating temperature of160° C., a crystallization-terminating temperature of 130° C., and aheat of crystallization of 49 J/g. The chip C1 also had a glasstransition temperature of 58.4° C. and a melting point of 204° C.observed as a single peak.

The chip Cl was further air-dried at 120° C. under a nitrogen atmosphereuntil absolutely dry and was then injection-molded into a sample stripwith the mold temperature kept at 140° C. Measurements taken of thesample piece gave a high-load distortion temperature of 132° C. Thesample piece also exhibited a high impact resistance.

Example 7

50 parts by weight of poly-L-lactic acid (“Lacty” manufactured byShimadzu Corporation, Mw=180,000), 50 parts by weight of poly-D-lacticacid synthesized from D-lactide (Mw=180,000), 1 part by weight of talcfine powder (Micro Ace P-6, manufactured by Nippon talc Co., Ltd.;Average particle size as determined by laser diffraction=4 μm), 0.5parts by weight of aluminumbis(2,2′-methylenebis-(4,6-di-tert-butyl-phenyl)phosphate).hydroxide,and 0.5 parts by weight of Li_(1.8)Mg_(0.6)Al₄(OH)₁₈CO₃.3.6H₂O, alithium-containing hydrotalcite compound, were dry-blended with oneanother, and the mixture was melted and mixed in a biaxial kneadingextruder at 220° C. for an average detention time period of 4 minutesand was extruded from a mouthpiece into strands. The strands were thenwater-cooled to obtain a chip C2 of a lactic acid-based polymercomposition.

The measurements taken of the chip C2 on a DSC gave a crystallizationpeak temperature of 171° C., a crystallization-initiating temperature of184° C., a crystallization-terminating temperature of 150° C., and aheat of crystallization of 58 J/g. The chip C2 also had a glasstransition temperature of 60.2° C. and a melting point of 209° C.observed as a single peak.

The chip C2 was further air-dried at 120° C. under a nitrogen atmosphereuntil absolutely dry and was then injection-molded into a sample stripwith the mold temperature kept at 170° C. Measurements taken of thesample piece gave a high-load distortion temperature of 150° C. Thesample piece also exhibited a high impact resistance.

Comparative Example 3

50 parts by weight of poly-L-lactic acid (“Lacty” manufactured byShimadzu Corporation, Mw=180,000), and 50 parts by weight ofpoly-D-lactic acid synthesized from D-lactide (Mw=180,000) were meltedand mixed in a biaxial kneading extruder at 220° C. for an averagedetention time period of 4 minutes and was extruded from a mouthpieceinto strands. The strands were then water-cooled to obtain a chip C3 ofa lactic acid-based stereo polymer composition.

The measurements taken of the chip C3 on a DSC gave a broad peak with acrystallization peak temperature of 118° C. (an inflection point alsoobserved at 138° C.), a crystallization-initiating temperature of 165°C., a crystallization-terminating temperature of 90° C., and a heat ofcrystallization of 37 J/g. The chip C3 also had a glass transitiontemperature of 58.4° C. and melting points observed as a double peak:168° C. for homo crystal and 215° C. for stereo crystal.

The chip C3 was further air-dried at 120° C. under a nitrogen atmosphereuntil absolutely dry and was then injection-molded into a sample stripwith the mold temperature kept at 120° C. Measurements taken of thesample piece gave a high-load distortion temperature of 70° C.

Comparative Example 4

50 parts by weight of poly-L-lactic acid (“Lacty” manufactured byShimadzu Corporation, Mw=180,000), 50 parts by weight of poly-D-lacticacid synthesized from D-lactide (Mw=180,000), and 1 part by weight oftalc fine powder (Micro Ace P-6, manufactured by Nippon talc Co., Ltd.)were dry-blended with one another, and the mixture was melted and mixedin a biaxial kneading extruder at 220° C. for an average detention timeperiod of 4 minutes and was extruded from a mouthpiece into strands. Thestrands were then water-cooled to obtain a chip C4 of a lacticacid-based stereo polymer composition.

The measurements taken of the chip C4 on a DSC gave crystallization peaktemperatures at 175° C. and at 134° C., crystallization-initiatingtemperatures at 190° C. and at 144° C., crystallization-terminatingtemperatures at 168° C. and at 130° C., respectively observed as adouble peak. The heats of crystallization were 38 J/g and 14 J/g,respectively. The peaks observed at higher temperatures than the otherof the double peaks are due to stereo crystals whereas the peaks atlower temperatures are due to homo crystals, indicating that theresulting sample was not in the state of complete stereo crystal. Thechip C4 also had a glass transition temperature of 59.3° C. and meltingpoints observed as a double peak: 170° C. for homo crystal and 218° C.for stereo crystal.

The chip C4 was further air-dried at 120° C. under a nitrogen atmosphereuntil absolutely dry and was then injection-molded into a sample stripwith the mold temperature kept at 170° C. Measurements taken of thesample piece gave a high-load distortion temperature of 75° C.

Shown in FIG. 1 is a chart depicting crystallization peaks taken on aDSC as the temperature was decreased, observed in Examples 6 and 7 andComparative Examples 4 and 5.

INDUSTRIAL APPLICABILITY

According to the present invention, a nucleating agent blended in apolylactic acid-based polymer accelerates the rate at which thepolylactic acid-based polymer undergoes crystallization withoutcompromising on the tensile strength or the impact strength.Furthermore, highly heat-resistant molded articles can be obtained byallowing the polylactic acid-based polymer composition to crystallize inmolds.

According to the present invention, a polylactic acid-based resincomposition is provided from which molded articles with a high tensilestrength, high impact strength and high heat resistance can be moldedwith improved moldability. Also provided is a heat-resistant polylacticacid-based resin molded article with an improved tensile strength andimpact strength, as well as a simple and highly efficient process formanufacturing such a heat-resistant molded article of polylacticacid-based resin.

According to the present invention, the inclusion of a metal phosphateto serve as a nucleating agent in a polymer capable of forming astereocomplex can increase the degree of crystallization of the lacticacid-based polymer. In a preferred embodiment, hydrous magnesiumsilicate (i.e., talc) is used along with a metal phosphate. Furthermore,highly heat-resistant molded articles can be obtained by allowing thelactic acid-based polymer composition to crystallize in molds.

According to the present invention, a polylactic acid-based resincomposition is provided from which molded articles with a high impactresistance and a high heat resistance can be molded with improvedmoldability. Also provided is a heat-resistant polylactic acid-basedresin molded article with an improved impact resistance, as well as asimple and highly efficient process for manufacturing such aheat-resistant molded article of polylactic acid-based resin.

1. A polylactic acid-based resin composition comprising 0.01 to 5.0parts by weight of a metal phosphate and 0.01 to 5.0 parts by weight ofa basic inorganic aluminum compound, each serving as a nucleating agent,with respect to 100 parts by weight of a polylactic acid-based polymer.2. The polylactic acid-based resin composition according to claim 1,wherein said metal phosphate comprises at least one metal salt of anaromatic organic phosphate represented either by the following generalformula (1):

wherein R₁ represents a hydrogen atom or an alkyl group having 1 to 4carbon atoms; R₂ and R₃ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₁ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₁ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₁ is an aluminum atom, or by the following general formula (2):

wherein R₄, R₅, and R₆ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₂ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.
 3. The polylactic acid-based resincomposition according to claim 1, further comprising as said nucleatingagent at least one selected from the group consisting of a dibenzylidenesorbitol compound represented by the following general formula (3) and ametal salt of an aliphatic carboxylic acid:

wherein R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms; and R₉ and R₁₀ each independently representa hydrogen atom or an alkyl group having 1 to 4 carbon atoms and may ormay not be identical to each other, provided that at least one of R₉ andR₁₀ is an alkyl having group 1 to 4 carbon atoms.
 4. The polylacticacid-based resin composition according to claim 1, wherein said basicinorganic aluminum compound is at least one selected from the groupconsisting of aluminum hydroxide, aluminum oxide, aluminum carbonate,and hydrotalcite compound.
 5. The polylactic acid-based resincomposition according to claim 4, wherein said hydrotalcite compound isrepresented by the following general formula (4):Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4) wherein a is anumber from 0 to 5.0; b is a number from 0 to 3.0; c is a number from0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a number from 0 to30.
 6. The polylactic acid-based resin composition according to claim 5,wherein said hydrotalcite compound is a lithium-containing hydrotalcitecompound with the amount a in the general formula (4) being in the rangefrom 0.1 to
 5. 7. The polylactic acid-based resin composition accordingto claim 1, further comprising hydrous magnesium silicate (talc).
 8. Thepolylactic acid-based resin composition according to claim 7, whereinsaid hydrous magnesium silicate (talc) has an average particle size of10 μm or less.
 9. A heat-resistant molded article of polylacticacid-based resin obtained by molding the polylactic acid-based resincomposition according to claim
 1. 10. A method for producing aheat-resistant molded article of polylactic acid-based resin, involvingthe steps of: melting the polylactic acid-based resin compositionaccording to claim 1, filling a mold of a molding machine set in atemperature range of not more than the crystallization-initiating pointnor less than the glass transition point, as measured by a differentialscanning calorimeter (DSC), with said composition, and molding saidcomposition under crystallizing.
 11. The method for producing aheat-resistant molded article of polylactic acid-based resin accordingto claim 10, wherein the temperature of said mold is set in atemperature range of not more than the crystallization-initiating pointnor less than the crystallization-terminating point, as measured by adifferential scanning calorimeter (DSC).
 12. A polylactic acid-basedresin composition comprising 100 parts by weight of a polylacticacid-based polymer and 0.01 to 5.0 parts by weight of a nucleatingagent, and having a crystallization peak temperature measured by adifferential scanning calorimeter (DSC) within the range of 90 to 120°C. and a heat of crystallization of 20 J/g or more.
 13. The polylacticacid-based resin composition according to claim 12, comprising as saidnucleating agent at least one selected from the group consisting of ametal phosphate and a basic inorganic aluminum compound.
 14. Thepolylactic acid-based resin composition according to claim 13, whereinsaid metal phosphate comprises at least one metal salt of an aromaticorganic phosphate represented either by the following general formula(1):

wherein R₁ represents a hydrogen atom or an alkyl group having 1 to 4carbon atoms; R₂ and R₃ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₁ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₁ is an alkali metal atom, analkaline earth metal atom or a zinc atom while q is an integer of 1 or 2when M₁ is an aluminum atom, or by the following general formula (2):

wherein R₄, R₅, and R₆ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₂ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.
 15. The polylactic acid-based resincomposition according to claim 13 further comprising as said nucleatingagent at least one selected from the group consisting of a dibenzylidenesorbitol compound represented by the following general formula (3) and ametal salt of an aliphatic carboxylic acid:

wherein R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms; and R₉ and R₁₀ each independently representa hydrogen atom or an alkyl group having 1 to 4 carbon atoms and may ormay not be identical to each other, provided that at least one of R₉ andR₁₀ is an alkyl group having 1 to 4 carbon atoms.
 16. The polylacticacid-based resin composition according to claim 13, wherein said basicinorganic aluminum compound is at least one selected from the groupconsisting of aluminum hydroxide, aluminum oxide, aluminum carbonate,and hydrotalcite compound.
 17. The polylactic acid-based resincomposition according to claim 16, wherein said hydrotalcite compound isrepresented by the following general formula (4):Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4) wherein a is anumber from 0 to 5.0; b is a number from 0 to 3.0; c is a number from0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a number from 0 to30.
 18. The polylactic acid-based resin composition according to claim17, wherein said hydrotalcite compound is a lithium-containinghydrotalcite compound with the amount a in the general formula (4) beingin the range from 0.1 to
 5. 19. The polylactic acid-based resincomposition according to claim 13, further comprising hydrous magnesiumsilicate (talc).
 20. The polylactic acid-based resin compositionaccording to claim 19, wherein said hydrous magnesium silicate (talc)has an average particle size of 10 μm or less.
 21. A heat-resistantmolded article of polylactic acid-based resin obtained by molding thepolylactic acid-based resin composition according to claim
 12. 22. Amethod for producing a heat-resistant molded article of polylacticacid-based resin, comprising the steps of: melting the polylacticacid-based resin composition according to claim 12, filling a mold of amolding machine set in a temperature range of not more than thecrystallization-initiating point nor less than the glass transitionpoint, as measured by a differential scanning calorimeter (DSC), withsaid composition, and molding said composition under crystallizing. 23.The method for producing a heat-resistant molded article of polylacticacid-based resin according to claim 22, wherein the temperature of saidmold is set in a temperature range of not more than thecrystallization-initiating point nor less than thecrystallization-terminating point as measured by a differential scanningcalorimeter (DSC).
 24. A polylactic acid-based resin compositioncomprising 100 parts by weight of a polymer (A) which is capable offorming a stereocomplex and is composed mainly of a polylactic acidcomprising a poly-L-lactic acid composed mainly of L-lactic acid and apoly-D-lactic acid composed mainly of D-lactic acid, and 0.01 to 5.0parts by weight of a metal phosphate as a nucleating agent forcrystllization.
 25. The polylactic acid-based resin compositionaccording to claim 24, further comprising 0.1 parts by weight or more ofa hydrous magnesium silicate (talc) to serve as said nucleating agentwith respect to 100 parts by weight of the polymer (A).
 26. Thepolylactic acid-based resin composition according to claim 25, whereinsaid hydrous magnesium silicate (talc) has an average particle size of10 μm or less.
 27. The polylactic acid-based resin composition accordingto claim 24, wherein said poly-L-lactic acid composed mainly of L-lacticacid comprises 70 to 100 mol % of L-lactic acid units and 0 to 30 mol %of D-lactic acid units and/or copolymer units other than lactic acid,and/or, said poly-D-lactic acid composed mainly of D-lactic acidcomprises 70 to 100 mol % of D-lactic acid units and 0 to 30 mol % ofL-lactic acid units and/or copolymer units other than lactic acid. 28.The polylactic acid-based resin composition according to claim 24,wherein said poly-L-lactic acid composed mainly of L-lactic acid has aweight average molecular weight of 50,000 to 500,000, and/or, saidpoly-D-lactic acid composed mainly of D-lactic acid has a weight averagemolecular weight of 50,000 to 500,000.
 29. The polylactic acid-basedresin composition according to claim 24, wherein the blend ratio byweight of said poly-L-lactic acid to said poly-D-lactic acid is in therange of 10:90 to 90:10.
 30. The polylactic acid-based resin compositionaccording to claim 24, wherein said metal complex comprises at least onemetal salt of an aromatic organic phosphate represented either by thefollowing general formula (1):

wherein R₁ represents a hydrogen atom or an alkyl group having 1 to 4carbon atoms; R₂ and R₃ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₁ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₁ is an alkali metal atom, analkaline earth metal atom or a zinc atom while q is an integer of 1 or 2when M₁ is an aluminum atom, or by the following general formula (2):

wherein R₄, R₅, and R₆ each independently represent a hydrogen atom oran alkyl group having 1 to 12 carbon atoms and may or may not beidentical to each other; M₂ represents an alkali metal atom, an alkalineearth metal atom, a zinc atom, or an aluminum atom; p is an integer of 1or 2; and q is an integer of 0 when M₂ is an alkali metal atom, analkaline earth metal atom, or a zinc atom while q is an integer of 1 or2 when M₂ is an aluminum atom.
 31. The polylactic acid-based resincompound according to claim 24, further comprising as said nucleatingagent at least one selected from the group consisting of a dibenzylidenesorbitol compound represented by the following general formula (3), abasic inorganic aluminum compound, and a metal salt of an aliphaticcarboxylic acid:

wherein R₇ and R₈ each independently represent a hydrogen atom or analkyl group having 1 to 4 carbon atoms and may or may not be identicalto each other, provided that at least one of R₇ and R₈ is an alkyl grouphaving 1 to 4 carbon atoms; and R₉ and R₁₀ each independently representa hydrogen atom or an alkyl group having 1 to 4 carbon atoms and may ormay not be identical to each other, provided that at least one of R₉ andR₁₀ is an alkyl group having 1 to 4 carbon atoms.
 32. The polylacticacid-based resin composition according to claim 31, wherein said basicinorganic aluminum compound is at least one selected from the groupconsisting of aluminum hydroxide, aluminum oxide, aluminum carbonate,and hydrotalcite compound.
 33. The polylactic acid-based resincomposition according to claim 32, wherein said hydrotalcite compound isrepresented by the following general formula (4):Li_(a)Zn_(b)Mg_(c)Al_(d)(OH)_(a+2b+2c+3d−2)CO₃.nH₂O  (4) wherein a is anumber from 0 to 5.0; b is a number from 0 to 3.0; c is a number from0.1 to 6.0; d is a number from 1.0 to 8.0; and n is a number from 0 to30.
 34. The polylactic acid-based resin composition according to claim24, wherein said polymer (A) which is capable of forming a stereocomplexcomprises an aliphatic polyester other than polylactic acid.
 35. Aheat-resistant molded article of polylactic acid-based resin obtained bymolding the polylactic acid-based resin composition according to claim24.
 36. A method for producing a heat-resistant molded article ofpolylactic acid-based resin, comprising the steps of: melting thepolylactic acid-based resin composition according to claim 24, filling amold of a molding machine set in a temperature range of not more thanthe melting point nor less than the glass transition point, as measuredby a differential scanning calorimeter (DSC), with said composition, andmolding said composition under crystallizing.
 37. The method forproducing a heat-resistant molded article of polylactic acid-based resinaccording to claim 36, wherein the temperature of said mold is set in atemperature range of not more than the crystallization-initiating pointnor less than the crystallization-terminating point as measured by adifferential scanning calorimeter (DSC).